Fingernails, as the human answer to claws in other animals, have many different functions. They are involved in protecting the sensitive fingertips, as well as providing fine precision gripping (for example, when you need to pull a splinter out of your skin).
Did you know? Fingernails grow at a rate of 1 mm per week; toenails at 0.2-0.5 mm per week
For both above functions, fingernails need to be very rigid, or hard. The bulk of the fingernail is made of a protein called keratin. This protein is very prevalent throughout the body, including in hair, teeth and skin. However, the fingernail contains a particularly high concentration of this protein, creating a very hard shell on the dorsal (back) side of the fingertip.
Did you know? Changes in the shape or colour of the fingernail or nail bed can be early indicators of health problems such as diabetes and liver or respiratory dysfunction (see link below).
For the most part, the keratin you see in your hair and fingernails is actually dead; in both cases, growth comes from protected living cells (called keratinocytes) below the surface of the skin, pushing the dead cells outward into view. This explains why trimming or cutting either your hair or fingernails does not hurt.
Did you know? A common myth is that fingernails and hair continue to grow after death; this is an optical illusion where dehydration of the body’s cells pull the fingers and skin away from the nails/hair, making it appear as if they are still growing.
Slide show – fingernails:7 signs of potential health problems
Fingernails and nutrition
What is keratin?